Heat exchanger for warm air furnaces



y 12, 59 L. BETZER 2,886,295

HEAT EXCHANGER FOR WARM AIR FURNACES Filed me 11, 1956 2 Sheets-Sheet 1i E a F/ 2 INVENTOR. g C/oyd L. Befzer His Attorney May 12, 1959 c.BETZER HEAT EXCHANGER FOR WARM AIR FURNACES Filed June 11, 1956 2Sheets-Sheet 2 INVENTOR. C/oyd L. Be/zer .2. C. 5% His Attorney UnitedStates Patent 2,886,295 HEAT EXCHANGER FOR WARM AIR FURNACES 'Cloyd L.Betzer, Rochester, N.Y., assignor to General Motors Corporation,Detroit, Mich., a corporation of Delaware Application June 11, 1956,Serial No. 590,725

2 Claims. (Cl. 257-139) This invention pertains to heat exchangers, andparticularly to heat exchangers for warm air furnaces.

Heretofore, heat exchangers for warm air furnaces have been made withexternally finned surfaces which increase the area of metal exposed tothe air to be heated, thereby increasing the rate of heat transferbetween the hot flue gases and the air to be heated. The presentinvention relates to an improved heat exchanger having integral internaland external fins so as to further increase the rate of heat transferbetween the hot flue gases and the air to be heated. With the improvedheat exchanger, the overall size of the heat exchanger for a furnace ofpredetermined capacity can be materially reduced. Accordingly, among myobjects are the provision of a heat exchanger having duplex finsurfaces; the further provision of a heat exchanger comprising aplurality of metal stampings, each stamping having integral internal andexternal fins; and the still further provision of a heat transferstamping having spaced, oppositely directed portions adapted toconstitute integral internal and external fins in an assembled heatexchanger.

The aforementioned and other objects are accomplished in the presentinvention by constructing the side, top, and bottom walls of a heatexchanger from a plurality of sheet metal stampings having oppositelydirected leg portions interconnected by a web portion. Specifically,each heat transfer stamping is formed from a flat strip, opposite edgeportions of which are bent in opposite directions and theinterconnecting web portion of which is bent to have a steppedconfiguration. Thereafter, the deformed strip is bent into a U-shapedsection.

In assembling the heat exchanger, the side, bottom and top walls areconstituted by the U-shaped sheet metal sections. The interconnectingweb portion of each section is telescopically received by the webportion of an adjacent section by reason of the stepped configuration ofthe web portions. Thereafter, the several sections are rigidly united byseam welding or furnace brazing. One sidewall, half of the top wall andhalf of the bottom wall of the heat exchanger are formed by one set ofU-shaped sheet metal sections, and the other sidewall, half of the topwall and half of the bottom wall are formed by another set of U-shapedsections. The two subassemblies may then be rigidly connected to form anintegral unit by seam welding.

The front and rear walls of the heat exchanger comprise dished sheetmetal stampings, the peripheral edges of which are seam welded to thetop, bottom, and sidewall unit. Preferably, the front and rear wallstampings have sheet metal fins welded to their exterior surfaces tofurther increase the heat exchange area. In addition, the front wallstamping has one or more openings adjacent its top and a lower openingarranged to accommodate a fuel burner.

The heat exchanger of this invention also constitutes the combustionshell of a warm air furnace. In a furnace installation, the combinedheat exchanger and combustion shell is enclosed by an outer casingwithin which a suitable 2,886,295 Patented May 12, 1959 blower ismounted. The blower discharges air to be heated across the outer surfaceof the heat exchanger, and hot flue gases are circulated through theinterior of the heat exchanger.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being bad to the accompanyingdrawings wherein a preferred embodiment of the present invention isclearly shown.

In the drawings:

Fig. 1 is a view, partly in section and partly in elevavation, takenalong line 1--1 of Fig. 2 of a warm air furnace having a heat exchangerconstructed according to this invention.

Fig. 2 is a fragmentary sectional view, taken along line 2-2 of Fig. 1.

Fig. 3 is a fragmentary perspective view, depicting the duplex finarrangement of the heat exchanger of this invention.

Fig. 4 is a fragmentary perspective view, of one of the duplex fin heatexchange sections.

With particular reference to Figs. 1 and 2, a warm air furnace is shownincluding an outer sheet metal casing 10, a centrifugal blower 12 beingmounted in the lower portion of the casing 10 and a combined heatexchanger and combustion shell 14 being mounted in the upper portion ofthe casing. As seen in Fig. 2, the blower 12 discharges air through anopening 16 in contiguous relation with the exterior of the combined heatexchanger and combustion shell 14. The air discharged by the blower 12flows upwardly across the exterior surface of the heat exchanger 14 andis discharged through an opening 18 in the top of the casing 10. Air issupplied to the blower through a suitable inlet opening, not shown.

The combined heat exchanger and combustion shell 14 includes a frontwall 20, a rear wall 22, as well as top, bottom, and sidewalls, theconstruction of which will be described hereinafter. The front wall 20has a lower 'opening at 24, into which a suitable gas burner 26 extends.

The gas burner 26 may be of any conventional design and is supported inthe casing 10 by any suitable means, not shown. The front wall 20 isformed with a pair of openings 28 and 30 adjacent the upper end thereofto which flue gas pipes 32 and 34 are connected. The combustion chamberflues 32 and 34 discharge into the space 70 and is mixed with airaspirated through the opening 72 in the casing 10 and the mixture passesout to the stack through stack pipe 36. The action is the same as thatof a drafthood well known in the art.

In addition, the front and rear walls 20 and 22 have welded thereto aplurality of sheet metal fins 38. The fins 38 increase the external heattransfer area of the heat exchanger 14 and thereby assist infacilitating the transfer of heat between the hot flue gases flowingupwardly through the interior of the heat exchanger and the air to beheated flowing across the exterior thereof.

With particular reference to Figs. 3 and 4, the novel duplex finarrangement of the side, top and bottom walls of the heat exchanger 14will be described. As seen in Fig. l, the top, bottom, and sidewalls ofthe heat exchanger are constituted by U-shaped sheet metal sections,such as indicated by numeral 40. Each intermediate U-shaped sheet metalsection has an outwardly directed fin portion 42, an inwardly directedfin portion 44, and an interconnecting web 46 of stepped configuration.Thus, the web 46 includes a portion 48 and a portion 50, the innersurfaces of which are located in spaced parallel planes. The externallyextending portion 42 and the internally extending portion 44 are locatedat substantially right angles to the interconnecting web 46. Inaddition, the ends 52 and 54 of the fin portions 42 and 44,respectively, are cut off at an angle, as shown more particularly inFig. 1, to

essence facilitate seam welding of the sections into an integral unit.

As seen in Fig. 3, the end section 4% adjacent the front of the heatexchanger has its outwardly directed fin portion 42 located at an angleof substantially 45 to the web 46. This arrangement facilitates itsinner connection with the front wall 20, which comprises a substantiallycup-shaped member having edge portions 56 and bent outwardly at an angleof 45. The end section 4% adjacent the rear wall of the heat exchangerdoes not include an internally extending fin portion since it isconnected to the rear wall member 22. in order to facilitate its connedtion with the rear wall member 52, the portion 44' is bent outwardly atan angle of 45 and cooperates with a similarly formed portion 53 on therear wall member 22.

In assembling the extended surface heat exchanger of the presentinvention, a plurality of the U-shaped sections 40 are assembled intelescopic relation, as shown in Fig. 3. That is, the portion of the web46 of one section is telescopcd over the portion 5% of the web 46 of thesection in front thereof. in other words, the U-shaped sections 40 areassembled in stacked relation, alter which they are seam welded, asindicated at 6% Since one set of U-shaped members 4%, when so assembled,forms one sidewall and half of the top and bottom walls, a complementaryset of sections is assembled to form the other sidewall and half of thetop and bottom walls. The two subassemblies are then seam welded alongthe top and bottom, as indicated by numeral 62 in Fig. 1. Thereafter,the front wall member 20 and the rear wall member 22 are attached byseam welding, as indicated by numeral 64 to complete the heat exchangerassembly.

By reason of the fact the heat exchanger of the present invention hasextended surface portions, or fins, on its interior and exteriorsurfaces, the overall size of the heat 0 exchanger can be materiallyreduced over that previously used for a given furnace capacity. Since inthe assembled heat exchanger, the hot flue gases transfer heat directlyto the internal fins, and since the internal fins are integral with theexternal fins, the heat transfer efiiciency of the heat exchanger isappreciably better than the prior heat exchangers wherein the fins weremerely attached to a shell and it was, thus, necessary to transfer heatby conduction through the joint between the fin and the shell.

From the foregoing, it is apparent that the present invention results inthe unique heat exchanger designed particularly for warm air furnaceshaving integrally finned interior and exterior surfaces. Moreover, byusing a heat exchanger construction of the type set forth herein, theoverall size of a heat exchanger for a given size furnace can bematerially reduced over that required with a conventional type heatexchanger.

While the embodiment of the present invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. A heat exchanger for warm air furnaces including,

a plurality of intermediate sheet metal sections constituting top,bottom and side walls of the heat exchanger, each intermediate sectionhaving integral internal and external extended surface portions and aninterconnecting web portion, means uniting said intermediate sections toform the top, bottom and side walls of the heat exchanger, a rear sheetmetal section attached to one of said intermediate sections having apair of integral external extended surface portions and aninterconnecting web, one of said ex ternal extended surface portionsbeing arranged at an acute angle relative to said interconnecting web, acupshaped rear wall having an edge portion complementary to the externalextended surface portion of said rear section located at an acute angleto said interconnecting web and attached thereto, and a front wallconnected to said intermediate sections, one of said walls havingopenings for the entrance and exit of hot flue gases.

2. A heat exchanger for warm air furnaces including, a plurality ofintermediate sheet metal sections constituting top, bottom and sidewalls of the heat exchanger, each intermediate section having integralinternal and external extended surface portions and an interconnectingweb portion, means uniting said intermediate section to form the top,bottom and side walls of the heat exchanger, a front sheet metal sectionattached to one of said intermediate sections having integral internaland external extended surface portions and an interconnecting web, theexternal extended surface portion of said front section being arrangedat an acute angle relative to its web, a rear sheet metal sectionattached to another of said intermediate sections having a pair ofexternal extended surface portions and an interconnecting web, one ofsaid external extended surface portions of said rear section beingarranged at an acute angle relative to its web, and a pair of cup-shapedend walls having edge portions complementary to the external extendedsurface portions of said front and rear sections which are located at anacute angle relative to their respective Webs and secured thereto, oneof said cup-shaped end walls having openings for the entrance and exitof hot flue gases.

References Cited in the file of this patent UNITED STATES PATENTS501,109 Smead July 11, 1893 1,777,782 Bundy Oct. 7, 1930 1,913,019Bluemel June 6, 1933 2,002,020 Nyborg May 21, 1935 2,028,298 Sucharskiet a1 Jan. 21, 1936 2,045,657 Karmazin June 30, 1936 2,566,161 BrownAug. 28, 1951 2,703,226 Simpelaar Mar. 1, 1955 FOREIGN PATENTS 324,654France Sept. 22, 1902 999,598 France Oct. 3, 1951

